1. Field of the Invention
The present invention relates to a high-frequency transformer in which coil elements are coupled to each other with a high degree of coupling, and a high-frequency component and a communication terminal device which including such a high frequency transformer.
2. Description of the Related Art
While a typical high-frequency transformer is formed by wrapping a primary coil and a secondary coil, which are made of metal wires, around a magnetic core made of ferrite or magnetic metal, it has been difficult for such a structure to be miniaturized.
On the other hand, for example, as described in Japanese Unexamined Patent Application Publication No. 2002-057042 or International Publication No. WO 2008/105213, a laminated high-frequency transformer has been known to include a primary coil and a secondary coil, formed by printing a conductor pattern of silver, copper, or other metal in a laminated body formed by laminating ceramic sheets. Since it is possible to manufacture such a laminated type high-frequency transformer using a sheet multilayer process where green sheets in which conductor patterns are printed are laminated and the laminated body thereof is subjected to co-firing, it is easy to manufacture the laminated high-frequency transformer, and it is also possible to miniaturize the high-frequency transformer.
FIG. 13 is a transparent perspective view of a laminated transformer 1 illustrated in International Publication No. WO 2008/105213. As illustrated in FIG. 13, the laminated transformer 1 includes a laminated body 2 and first to fourth external electrodes 3-1 to 3-4. Specifically, a primary coil 4 and a secondary coil 5 are pattern-formed in a predetermined layer of an insulator 6, and the first to fourth external electrodes 3-1 to 3-4 are formed on end surfaces of the laminated body 2.
One shortcoming of the above-described sheet multilayer process is that there is a limit as to available materials which can be used. In other words, it is difficult to make green sheets using a magnetic material whose saturation magnetic flux density or magnetic permeability is high, and it is difficult to subject the green sheets to co-firing along with a conductor pattern material. Therefore, it is difficult to use a magnetic material whose saturation magnetic flux density or magnetic permeability is high, and it is difficult to obtain a high-frequency transformer having a high coupling coefficient and a low loss.